<div class="loader">
  <div class="circle circle-1"></div>
  <div class="circle circle-2"></div>
  <div class="circle circle-3"></div>
  <div class="circle circle-4"></div>
</div>

<style>
/* From Uiverse.io by Diox221 - Tags: loader, accept call */
.loader {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100%;
}

.circle {
  position: relative;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  margin: 10px;
  box-shadow: inset 0 0 0 2px #fff;
  transform-origin: center;
  animation: fill 1.5s ease-in-out infinite;
}

.circle-1 {
  animation-delay: 0s;
}

.circle-2 {
  animation-delay: -0.4s;
}

.circle-3 {
  animation-delay: -0.8s;
}

.circle-4 {
  animation-delay: -1.2s;
}

@keyframes fill {
  0% {
    transform: scale(1);
  }

  50% {
    box-shadow: inset 0 0 0 2px #fff, inset 0 0 0 6px #1c1c1e;
    transform: scale(1.5);
  }

  100% {
    box-shadow: inset 0 0 0 2px #fff, inset 0 0 0 6px #fff;
    transform: scale(1);
  }
}

</style>
